Method of forming spark-plugs.



UNITED 1 STATES PATENT OFFICE.

ALBERT SCHMIDT, 0F FLINT, MICHIGAN, ASSIGNOR TO CI-IAMPION IGNITION COMPANY, OF FLINT, MICHIGAN, A CORPORATION OF MICHIGAN.

METHOD OF FORMING SPARK-PLUGS.

Specification of Letters Patent.

Patented July 24, 191 '7.

. Application filed January 18, 1917. Serial No. 143,147.

To all whom it may concern: i

Be it known that I, ALBERT SCHMIDT, a citizen of the Republic of France, residing at Flint, in the county of Genesee and State of Michigan, have invented certain new and useful Improvements in Methods of Forming Spark-Plugs,of which the following is a specification, reference being had therein to the accompanying drawings.

The invention relates to the manufacture of spark-plugs, and has particular reference to the method of forming a gas-tight seal between the insulator and the electrode or other metallic part of the structure.

In the present state of the art great difficulty is experienced in producing a plug which will be free from leakage under all conditions of use, and particularly where used with high-speed engines. This difliculty is chiefly due to a differential expansion in the metallic parts and insulation, so that a plug which is gas-tight at ordinary temperatures will often leak when highly heated. Another difficulty is due to the unavoidable irregularities in the surface of the insulator upon which the sealin flange is seated, so that where adjustment is made,- disturbing the contact, leaks are often formed. As a specific instance, it is common to secure the electrode which passes centrally through the insulator by a threaded nut orcap, which is seated on the insu lator and is designed to form a seal as well as a means of ad ustment; but when adjustment is made the shifting of the bearing frequently produces leakage.

With the present invention these difiiculties are overcome by a method of sealing, in which the metal part is exactly-conformed *th e ofthe insulatpr upon which it bears,'and further is placed under resili ent tension-so that it will maintain its scat even where differential expansion takes place.

In the drawings:

Figure'l is a section through a portion of a spark-plug with the electrode in initial engagement with the insulator before the sealing operation;.

Fig. 2 is a similar view illustrating the method of sealing;

Fig. 3 is a plan View of Fig. 2;

Fig. 4 is a diagram. illustrating the manner in which the sealis maintained where expansion takes place.

.sulator.

ving a groove F therein.

collar on the electrode, providing a shoulder for bearing against the outer end of the inlVith the construction as thus far described, when the threaded portion C is en aged with the threaded recess D, the co lar E may be tightened against the end of the insulator; but it is difficult to form a gas-tight seal on account of the irregularities in the insulator surface. By placing a compressible gasket between the shoulder and the insulator, a seal may be made, but when the plug is heated and the metal expanded leakage will occur. This I avoid by sealing in the following manner: 1

After the electrode has been secured down to cause the collar E to bear upon the insu-' lator, the periphery of this collar is rolled or otherwise subjected to a pressure for form- As specifically shown, a series of grooving rolls G are mounted on a suitable instrument (not shown), and caused to rotate about the periphery of the collar, and at the same time to bear inwardthereon. Each of these rolls has a periphery of V-shaped cross-section, so that as it is forced into the metal of the collar said metal will be deflected in o posite directions. The inner portion wil be pressed against the insulator and fashioned intov exact conformity to the surface thereof, while the lateral deflection of the outer portion will place the same under tension. Preferably the mass of the metal on the outer side of the groove'is greater than that on the inner side, so that when relieved from the pressure of the rolls it will spring inward,

is placed is sufiicient to compensate for this expansion and to maintain the tight joint.

W I claim as my invention is: 1. e method of forming a gas-tlght joint between a metallic and a non-metallic part of a spark-plug, comprising the initial seating. of the metallic part on the non-me tallic part, and subjecting the metal to pressure for deflecting portions thereof oppositely, one portion being conformed to the surface of the non-metallic part a'gainst which it bears, and the other portion being placed under tension for holding the first-' lfnentioned portion against its bearing surace.

-2. The method of forming a gas-tight jointbetween a metallic and a non-metallic part of a spark-plug, comprising the initial seating of the metallic part on the non-metallic part, and peripherally rolling the metallic part to 'form a groove therein, deflecting the metal on one side of said groove to collar to deflect the metal oppositely, the

metal on the side of the groove adjacent to the side of the insulator being compressed into exact conformity to the surface against which it bears and the metal on the opposite side of the groove being placed under resilient tension.

' 4. In a spark-plug, the combination with the insulator and a metallic part to be secured thereto, of a collar von said metallic part, peripherally grooved to conform the metal on one side of the groove exactly to the surface of the insulator, the metal on the opposite side of the groove being under resilient tension.

5. In a spark-plug, the combinatlon with an insulator, of an electrode having a threaded engagement with said insulator, and a collar seated upon the end of the insulator, said collar being peripherally grooved, the metal on one side of the groove being conformed to the surface of the insulator and I the metal on the opposite side of the groove being under resilient tension.

In testimony whereof I afix my signature.

ALBERT SCHMIDT. 

